My dispensational leaning prompted me to respond here. Scripture is certainly the mainstay to doctrine in this dispensation, however it was not the first means that God chose, nor do I believe that it will be the last.
God began dispensing grace in the garden when he killed animals instead of Adam and Eve. I think that Adam and Eve had some measure of understanding of grace, perhaps greater than we have today. Though they did not know Jesus, the man, they were looking ahead for him.
Scripture was added much later.
"In the beginning was the Word, and the Word was with God, and the Word was God." -- John 1:1